The present invention relates to a plasma etching method, and more particularly to a plasma etching method that can reduce the amount of active gas that is used for etching and PFC that is a global warming gas.
Conventionally, in the process for manufacturing semiconductor devices, etching that partially cuts a semiconductor wafer or material deposited thereon is frequently used. Plasma etching sputter etching or reactive ion etching methods are known ways to perform the etchings. In particular, plasma etching uses chemical reaction such that only materials that need to be etched are removed (in other words selectively etched). For this reason, plasma patching is widely used in the process of manufacturing semiconductor devices.
FIG. 5 shows an illustration to describe a structure of a chamber in which plasma etching is conducted. Electrodes that generate plasma are disposed within the chamber 1, and the electrodes are connected to a high-frequency plasma generation apparatus that is provided outside the chamber. Also, within the same chamber 1, a semiconductor wafer mounting section is provided, such that a semiconductor wafer and material deposited thereon can be etched.
The chamber 1 described above is equipped with a reactive gas supply opening 2 and an exhaust opening 3 as shown in the figure, whereby a reactive gas can be introduced into the chamber 1 under a reduced pressure through a flow quantity control valve 4, and the reactive gas can be exhausted from the chamber 1 by a vacuum pump (not shown) provided in the succeeding stage of the exhaust opening 3. PFC such as CF4, CHF3, C4F8 or the like is used as the reactive gas to conduct an etching of silicon oxide (SiO2) that is used as a dielectric material.
FIG. 6 shows a graph of an operation process of the chamber 1. As shown in the figure, for conducting an etching on a semiconductor wafer within the chamber 1, first, the pressure within the chamber 1 is sufficiently reduced by the vacuum pump (a range {circle around (1)} in the figure), and the flow quantity control valve 4 is opened to introduce a reactive gas into the chamber 1. As the reactive gas is introduced into the chamber 1, the reactive gas is also discharged through the exhaust opening 3. It is noted that, when the reactive gas is introduced, the degree of opening and closing of the flow quantity control valve 4 is adjusted, such that the pressure within the chamber 1 is adjusted to stabilize at a predetermined value (a range {circle around (2)} in the figure).
After the pressure within the chamber 1 is stabilized at the predetermined value, the high frequency plasma generation apparatus is operated to generate plasma of the reactive gas between the electrodes, whereby an etching process for the semiconductor wafer is conducted (a range {circle around (3)} in the figure). When a predetermined time has passed, the flow quantity control valve 4 is closed to stop the supply of the reactive gas, and the high frequency plasma generation apparatus is also stopped to complete the etching process (a range {circle around (4)} in the figure).
However, in the etching process described above, the following problems are encountered. In a preceding stage of the etching (the range {circle around (2)} in the figure), the pressure within the chamber 1 needs to be set at a predetermined value, and a reactive gas that is used for the plasma process is used for setting this value. In other words, during the pressure setting within the chamber, a reactive gas that does not contribute to the plasma etching is exhausted through the exhaust opening 3 into the atmosphere as it is. This results in a higher cost. Further, since the PFC that is used as a reactive gas has a high GWP (global warming potential) that is several thousandsxe2x80x94several ten thousands times higher than that of carbon dioxide, it is not preferable for the environment to exhaust the gas into the atmosphere.
The present invention has been made in view of the problems of the conventional art, and it is an object of the present invention to provide a plasma etching method that can suppress discharge of PFC that does not contribute to the plasma etching into the atmosphere.
The present invention has been made based on knowledge that, when a pressure adjustment in the chamber is conducted by material other than PFCs (perfluorocarbon and compounds thereof (HFC) in which part of PFC is replaced with hydrogen), and the material is switched to PFC after the pressure adjustment is completed, PFC that does not contribute to plasma etching can be discharged into the atmosphere.
Namely, a plasma etching method is characterized in that: an inactive gas is passed into a chamber under a reduced pressure; after the chamber is set to a specified pressure, the inactive gas is switched to an active gas and plasma is generated in the active gas; and an etching of a semiconductor wafer disposed in the chamber is conducted.
In the plasma etching method, since the pressure adjustment within the chamber is conducted using an inactive gas, an active gas does not need to be used for the pressure adjustment, the amount of the active gas to be used can be reduced, and an active gas that does not contribute to the etching is prevented from being discharged into the atmosphere. Also, in accordance with the present method, only the process for adjusting a pressure within the chamber is changed, and the etching process is not changed. Accordingly, the amount of an active gas to be used can be reduced without changing the characteristics of the etching itself. It is noted that, after the pressure adjustment, an active gas in the same amount as that of the inactive gas may be introduced into the chamber, so that the etching is conducted by the introduced active gas within the chamber.
Another plasma etching method is characterized in that: an inactive gas is passed into a chamber under a reduced pressure; after the chamber is set to a specified pressure, plasma is generated in the inactive gas; after the plasma is generated, the inactive gas is switched to an active gas; and an etching of a semiconductor wafer disposed in the chamber is conducted. In the plasma etching method, since the pressure adjustment within the chamber is conducted using an inactive gas, an active gas does not need to be used for the pressure adjustment, the amount of the active gas to be used can be reduced, and an active gas that does not contribute to the etching is prevented from being discharged into the atmosphere. Also, plasma is generated in the inactive gas after the pressure is adjusted, and then the inactive gas is switched to an active gas (the inactive gas is replaced with an active gas in the same amount). Therefore, plasma is generated in the active gas as the active gas is introduced (under the influence of the plasma inactive gas). As a result, no time is needed from the introduction of the active gas until the stabilization of the plasma such that the active gas can be used for the etching without being wasted.
Also, in accordance with the present method, only the process for adjusting a pressure within the chamber is changed, and the etching process is not changed. Accordingly, the amount of an active gas to be used can be reduced without changing the characteristics of the etching itself.
Yet another plasma etching method is characterized in that: an inactive gas is passed into a chamber under a reduced pressure; after the chamber is set to a specified pressure, plasma is generated in the inactive gas and at the same time an active gas is introduced into the chamber; and an etching of a semiconductor wafer disposed in the chamber is conducted using plasma generated in a mixed body of the inactive gas and the active gas.
In the plasma etching method, since the pressure adjustment within the chamber is conducted using an inactive gas, an active gas does not need to be used for the pressure adjustment, the amount of the active gas to be used can be reduced, and an active gas that does not contribute to the etching is prevented from being discharged into the atmosphere. Also, plasma is generated in the inactive gas after the pressure is adjusted, and then the inactive gas is switched to an active gas. Therefore, plasma is generated in the active gas as the active gas is introduced (under the influence of the plasma of the inactive gas). As a result, no time is needed from the introduction of the active gas until the stabilization of the plasma, such that the active gas can be used for the etching without being wasted. This example uses a process that includes not only an active gas but also an inactive gas as a base etching condition, such that the inactive gas does not need to be completely switched to the active gas. Also, since the inactive gas is continuously introduced from the time of the pressure adjustment, the pressure within the chamber and the generated plasma can be stabilized.
Also, for the purpose of maintaining the pressure within the chamber constant, when the inactive gas is switched to the mixed body of the inactive gas and the active gas, the flow quantity of the inactive gas is restricted by a specified amount, and the active gas is introduced in an amount corresponding to the amount of the reduced inactive gas, such that the overall flow quantity becomes constant.
Another plasma etching method is characterized in the active gas is PEG. As a result, the amount of PFC to be used can be reduced and PEG that does not contribute to the etching is prevented from being discharged into the atmosphere.
Still another plasma etching method is characterized in that the inactive gas is helium. Since helium has a small atomic weight among inactive gases, when plasma is generated in helium, the influence that may be inflicted on semiconductor wafers and the internal walls of the chamber can be reduced (sputtering or the like does not occur).